Electrode for electrolytic shaping



75inch 5 1 L. A.WILLI I'\MY S ELECTRODE FOR ELECTROLYTIC SHAPING 1 2Sheets-Sheet 1 Original Filed Nov. 10, 1958 3,498,904 ELECTRODE FORELECTROLYTIC SHAPING Lynn A. Williams, Winnetka, Ill., assignor toAnocut Engineering Company, Chicago, 10., a corporationof 1015Application Feb. 14, 1966, Ser. No. 552,652, now Patent No. 3,421,997,which is a continuation of application Ser. No. 165,569, Jan. 11, 1962,which in turn is a division of application Ser. No. 772,960, Nov. 10,1958, now Patent No. 3,058,895, dated Oct. 16, 1962. Divided and thisapplication Jan. 2, 1969, Ser. No. 788,482

Int. Cl. B23p 1/02; B01k 3/04 US. Cl. 204-284 Claims ABSTRACT OF THEDISCLOSURE CROSS-REFERENCES TO RELATED PATENTS This application is adivision of my application Ser. No. 552,652, filed Feb. 14, 1966, nowPatent No. 3,421,- 997, which application is a continuation of myapplica tion Ser. No. 165,569, filed Jan. 11, 1962, now abandoned, whichapplication is a division of my application Ser. No. 772,960, filed Nov.10, 1958, entitled Electrolytic Shaping now issued into Patent No.3,058,895, dated Oct. 16, 1962.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to electrodes for use in electrochemically shaping metal andmetalloid materials.

Description of the prior art It has long been known that metal andmetalloid materials may be removed by electrolytic attack in aconfiguration where the metal or metalloid workpiece is the anode in anelectrolytic cell. This principle has been used industrially to somedegree for the removal of defective plating and the like, and issometimes referred to as stripping. It has also been used to some extentfor electrolytic polishing, in which application, however, the principalpurpose is to produce a smooth finish with a minimum removal of the workmaterial. Here the purpose is to remove substantial amounts of metalrapidly and with accuracy.

SUMMARY OF THE INVENTION In the present instance, the term metalloid isused somewhat specially in referring to those electrically conductivematerials which act like metals when connected as a anode in anelectrolytic cell and are capable of being electrochemically eroded. Theterm as used here and in the claims includes metals and such similarlyacting materials as tungsten carbide, for instance, and distinguishesfrom such conductive non-metalloids as carbon.

George F. Keeleric has proposed in his Patent No. 2,826,540, issued Mar.11, 1958, for Method and Apparatus for Electrolytic Cutting, Shaping andGrinding the use of electrolysis in conjunction with a metal bonded,abrasive bearing, moving electrode, and the method and United StatesPatent O 3,498,904 Patented Mar. 3, 1970 apparatus of this Keelericpatent have found extensive industrial use.

The present invention departs from the teachings of Keeleric inutilizing relatively fixed or slow moving electrodes without abrasive,and is intended for work of a quite different character, as will appearin the detailed description of the invention which follows:

In general, in the present invention an electrode, quite frequently ahollow electrode, is advanced into the work material by mechanical meanswhile electrolyte is pumped through the work gap between the electrodeand the work, and at times the hollow portion of the electrode, undersubstantial pressure. In some circumstances, the side walls of theelectrode are protected by an insulating material so as to minimizeremoval of work material except where desired. Various forms ofelectrodes are used for different kinds of Work, and likewise differenttechniques advancing the electrode toward and into the work material areused, depending upon the nature of the operation to be performed. In thepresent application porous metallic electrodes are the subject of theinvention.

An important aspect of the invention lies in providing electrodes inwhich a flow of electrolyte between the electrode and the work ismaintained at high velocity and across a short path between the point ofentry and the area of exit regardless of the over-all size of theelectrode. An electric current is supplied so that current passes fromthe electrode, which is negative, through the electrolyte to theworkpiece, which is positive. For purposes of shaping the electrodes,direct current may be passed in the opposite sense to make the electrodepositive. In some instances, alternating current may be used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of oneform of apparatus utilizing the electrode of the present invention;

FIG. 2 is a diagrammatic representation of an electro lyte supply systemwhich forms a portion of the apparatus of FIG. 1;

FIG. 3 is a longitudinal sectional view through an electrical tip whichmakes use of a porous metal element at the working face thereof;

FIG. 4 is a perspective View of the working end of another electrode inwhich the working tip is formed of a porous metal and particularlyadapted for sinking cavities or comparatively large areas; and

FIG. 5 is a transverse sectional view taken along the line 55 of FIG. 4looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, theapparatus includes a frame member 1 which in this instance is the framemember of a conventional and well known arbor press sold under the tradename of FAMCO. It includes a base section 3, a column 5, and a head 7which is adapted in the conventional manner to accommodate a ram 9 forvertical reciprocating motion. The detail of the ram mounting is notimportant to this invention, but it is desirable to provide adjustablegibs or the equivalent in the head so that the ram may move verticallywith a smooth action and without lateral play which might introduceundesired side motion. To the bottom end of the ram 9 there is mounted aworkplate 11 through which a plurality of bolt holes is provided topermit adjustable mounting of a work-holding vise 15.

On the base portion 3 there is mounted a metal bottom plate and on topof this a waterproof, chemicalresistant plastic mounting plate 19. Thisis provided with a number of threaded bolt holes to permit mounting ofan electrode holder 21, which is made of suitable metal and is providedwith one or more mounting slots so that 3 r it can be adjusted as to itsposition by'selection of the suitable bolt holes in mounting plate 19.

At the working end, the electrode support member 21 is hollow and isadapted to receive an electrolyte feed tube fitting 27 connected to aline leading to a source of electrolyte under pressure.

Extending from the upper surface, there is mounted on electrode 31,shown here as fastened by brazing to a pipe nipple threaded into theelectrode support member 21. Within the hollow support member 21 theelectrode is connected by a suitable passage to the feed tube fitting27.

An electric cable is connected to the electrode block or support member21 and supplies current from the power source. Another electric cable 35is fastened to work plate 11 to furnish the other (normally positive)connection from the power source.

To move the work plate 11 up and down, a lead screw 37 is secured to andextends upwardly from the upper end of the ram 9. A lead nut 39 isthreaded upon the lead screw and is mounted between two horizontalplates 41 which are supported by four column bars 43. The lead nutperipherally is formed as a worm gear so that it may be rotated to movethe lead screw 37 up and down. A journal plate 45 is mounted to theplates 41 and carries a bearing bushing 47 which supports the outboardend of a drive shaft 49 which carries worm 51 meshed with the peripheralworm gear of lead nut 39.

The worm drive shaft 49 is in turn rotated by 21 variable speed electricmotor drive 53 mounted upon a platform 55 attached to the column 5. Thisdrive mechanism has a speed adjusting handle 57 and a reversing handle59, the latter having a neutral mid-position as well as updrive anddowndrive positions.

The sizes and proportions of the drive parts are arranged to permitadjustment in the vertical speed of movement of the work plate 11 fromzero to one inch per minute. The motion must be smooth, not jerky, andaccordingly, reasonable accuracy and freedom from excessive friction arean advantage in the moving drive parts. The lead screw 37 may beprotected against splatter and corrosion by a plastic enclosure 61wrapped around the column bars 43.

A conventional dial indicator 63 is shown as mounted to the head 7 ofcolumn and has its working tip extended downwardly against the uppersurface of work plate 11 so as to indicate relative movement as betweenthese elements.

The entire assembly is mounted in a pan 65 which has an outlet spudadapted to drain electrolyte back into a supply sump or reservoir 74.The work plate 11 is fitted with plastic curtains 71 which can be tuckeddown below the level of the pan top to prevent excessive splatter.

The plumbing system (FIG. 2) comprises a low pressure pump 73 whichfeeds electrolyte from the reservoir 74 through a filter 75 into highpressure pump 77, the outlet of which leads to a bypass valve 79 whichmay be either manually set or of the spring loaded constant pressuretype. On the inlet side of the bypass valve 79 a pressure gauge 81 ismounted. Also from the inlet side, a pipe .lead is taken through aneedle valve 83 to an electrolyte feed tube 84 leading to the electrodefitting 27. A secondtgauge 29 is connected to the feed tube 84 so as toindicate the pressure at the electrode.

, In operation, a workpiece is positioned in the vise 15 above theelectrode 31, and the work plate 11 is then driven down until theworkpiece is almost touching electrode 31 as gauged by a piece of paperor shim of known thickness, say .003 inch. The dial indicator 63 is thenadjusted to zero minus the known thickness, .003 inch in this example.The curtains-'71 are lowered ,or otherwise closed, the electrolyte pumps73 and 77 are started, and the valves 79 and 83 are adjusted so thatgauge 81 reads about 120 p.s.i. and gauge 29 about 90 p.s.i. This is.done while thereversing handle 59 is in neutral positionThen,

simultaneously, the reversing handle is moved to downdrive position, andthe electric power supply is turned on.

As the electrode approaches the workpiece, there will be a rise inpressure at the gauge 29. If the capacity of pumps 73 and 77 is severaltimes the free flow discharge rate through the electrode, the pressureupstream of the needle valve 83 and of bypass valve 79 as read at gauge81 will change scarcely at all wtih changes in proximity of theelectrode 31 to the work, for most of the flow is passing through bypassvalve 79, and it is the adustment of this which is principallydeterminative of the pressure at gauge 81. In short, the pumps andplumbing system up to needle valve 83 constitute a substantiallyconstant pressure source. The same result may be obtained in many otherways. A constant pressure type pump may be used, e.g., a centrifugalpump operating near cutoff. Or a pressure regulator may be used. Or aspring loaded relief valve adapted to maintain constant pressure maybeused.

Needle "valve 83, however, is set so as to constitute a sufiicientrestriction to flow'so that when the electrod is discharging into theopen, the pressure as read at gauge 29, will be noticeably lower thanwhen its outlet is restricted by being in. close proximity to the work.

Thus, if gauge 81 normally reads 120 p.s.i., then when the electrode 31touches the workpiece so as to shut off the flow, or nearly so, thepressure downstream of needle valve 83 as read at gauge 29 will rise toalmost the same value, 120 p.s.i. If, however, the electrode 31 isspaced away by several thousandths of an inch, the pressure at gauge 29will drop, say to 90 p.s.i.

This change in liquid pressure may be used in adjusting the rate of feedof ,the work toward the electrode. The initial feed rate may be set at alow level (for an unknown working condition or work material) and thenincreased by adjustment of the handle 57. Gauge 29 is observed to watchfor a pressure rise which approaches that of gauge 81. It takes a littletime for the pressure reading to stabilize during actual removaloperations, for inasmuch as material is being removed by anodicdissolution, it is necessary for the moving electrode to catch up withthe receding work material and to establish an equilibrium spacingdistance, for as the electrode comes closer to the work, the removalrate tends to increase. By the exercise of reasonable care, it ispossible to make a precise adjustment such that the electrodepressure-gauge 29 reads only a few pounds per square inch lower thangauge 81, indicating that the electrode is moving forward at such a rateas to leave only a small gap between the electrode and the work.

In effect, this hydraulic system constitutes a flow meter, and. the sameresult-may be obtained by using a more formal flow meter to sense theflow rate through the gap between the electrode and the work. Such flowmeter may be of any suitable sort, as for instance of the orifice type(which, in eflect, uses the principle of the system just described) orof some. other type, for example, that in which amoving bob is supportedby upward flow in a conical glass vessel (e.g., the Fischer and Portertype).

It isnot easy to measure this gap with accuracy, as apparently it is notalways uniform at every point, but as measured in a practical way, byturning off the current and advancing the electrode until it seems tobottom, the

7. distance maybe as small as .001 inch or less, to as much as .010inch, with satisfactory results, although it is preferred to work withthe shortest spacing distance which can be managed without causingoccasional contact and arcing between the electrode and the work, and Ihave found that about .002 inch to .005 inch is usually a safe distance'while still permitting rapid removal of work material. 7

In general, low voltages and close spacing, of the order of. .001 inchto .005 inch, 'give high removal rates and low electric power costs anda higher degree of accuracy, but less striation is produced upon theside wall of the work cavity when greater spacing, of the order of .010inch, is used. The greater spacing results in a lower work removal rateunless the voltage is raised however, since removal rate is a functionof current. As a practical matter in most applications, I prefer to useabout volts and from 100 to 3000 amperes per square inch of activeelectrode area.

It should be noted that work material is removed by electrolytic action,not by spark or arc erosion, as with the so-called electrodischargemethod. This is important for several reasons, among them the fact thatdamaging thermal metallurgical effects on the work material are avoidedand that there is virtually no erosion of the electrode. The fact thatthe electrode is not eroded is of great importance where the cavity isto be accurately shaped,

for accurate shaping is rendered very difiicult when the electrode isbeing eaten away at a rate rapid enough to alter its dimensions duringthe operation.

Thus, it is important to avoid too fast a feed rate which may causearcing between the electrode and the work.

Another method of gauging the feed rate is by reference to an ammeter inthe electrolytic power supply circuit. Once the penetration of theelectrode into the work has been well established, the rate of feed isgradually increased until an arc is observed. Usually this will be ofshort. duration. The reading of the ammeter is ob served and read justprior to the first arc, and the speed is then adjusted downwardly untilthe ammeter shows a reading of little below the critical point where thefirst arc occurred.

A transducer sensitive to either the electrolyte liquid flow rate or theelectrolytic electric current may be used as the signal generatingelement in an automatic feed control system. 1

FIG. 3 shows in section an electrode end in which the porous metalmember 321has been fastened by rolling the tube body 275 into an annulargroove 322 in the porous metal element, which is also shaped to form.the working lip 281. Ceramic coating 283 is then applied to the exteriorof the electrode.

This electrode is suitable for small areas, but I have found that whenthe diameter of a porous metal type of electrode tip is as large as 1inch, thework is left with radially extending grooves probablycaused byliquid exitingv irregularly from the mid-area of the tip. The path fromthe point of introduction of electrolyte to the point where it leavesthe active work area should preferably be kept short, and I prefer tokeep this distance under /s inch to M4 inch. v

When it is desired. to produce cavities having a better finish, I prefer-to use electrodes constructed generally after the fashion illustratedin FIGS. 4, and 5. The electrode of FIGS. 4 and 5 is essentially similarto the one shown in FIG. 3 in that a piece of porous metal 321 issecured at the working end of a tubular electrode member 275. It ispreferable, however, for use in forming cavities of larger size than theelectrode illustrated in FIG.,3, since it provides for an escape of theelectrolyte from the interface between the electrode tip and the work.

The porous metal member 321 is provided with one or more transverseholes 339 which are connected to the working face of the electrode by aplurality of smaller holes 341. The electrolyte, therefore, underpressure within the tube 275 finds its way to the working face of theelectrode through the tortuous passages within the porous member 321,and this electrolyte then escapes by way of the small passages 341 tothe larger channels 339 which carry the electrolyte away from'the work.If it is found that an excessive amount of electrolyte escapes directlyinto the channel 339, for instance, without reaching the work, thesechannels can be sealed as by burnishing, for instance, and thistreatment may also be given to the smaller passages 341 so that althoughthere may be some leakage directly into these passages, such leakage isa minor consequence. Alternatively these surfaces may be lightly tinnedwith solder or plated to effect the seal.

All of the electrodes discussed above may be relieved to a shallow depthat their side faces, and this recessed portion may be coated with aceramic layer which is for the purpose of inhibiting side action asbetween the electrode and the side walls of the cavity. Furthermore, theend face of this and other electrodes may be shaped by deplating; thatis, by reversing the current and plating away the end face of theelectrode as it approaches a shaped tool which has a contour which isthe negative of the contour desired upon the electrode.

The purpose of the enamel coating is to utilize its insulatingproperties to minimize electrolytic side action between the electrodebody and the side walls of the cavity.

Vitreous enamel is the best coating I have found, but other insulatingmaterials may be used. I have found Teflon quite satisfactory where itcan be easily applied. However, the organic lacquers and paints whichhave been tested have not been very satisfactory because they seem .tobe chemically or physically attacked near the working tip. The vitreousenamel seems to be quite impervious to such deterioration.

Copper is a good substance for forming the electrode because it is agood electrical conductor, but good success has been had with coldrolled steel. Brass may be used, but it is ditficult to get a goodvitrified enamel coating on brass, and accordingly, it is not preferred.All of these materials are, in general, somewhat less satisfactory thanstainless steel or titanium in that they are susceptible to theformation of plating deposits which, under some conditions, may make theoutline of the electrode less clean, and in some instances such depositsmay change the current fiow characteristics of the system.

From the above description of my invention which has been illustrated inseveral embodiments and variations, the features and applications of theinventive idea to practical problems have been discussed. From this itwill be apparent that certain generalizations may be made.

The amount of metal removed from a workpiece by electrolytic action is adirect function of the current in the electrolyzing circuit. The voltagenecessary to pass any particular current with any particular set ofcircumstances will'depend upon the spacing between the electrode and theworkpiece. It will also depend upon the electrode size or effectivearea, but for a particular job the electrode size usually will not be avariable.

The cost of operation will vary rather directly with the wattagethat is,the amperage in the circuit times the voltage necessary to produce thecurrent. From these con-' siderations it follows that from the practicalstandpoint it is'essential that the electrode to workpiece spacing beheld to a practical minimum so that minimum voltages may be used,thereby enabling the operation to be conducted at minimum cost. As anexample, by following the teachings of the present invention, preciselyheld small spacings may be used and most electrolyzing operations may beconducted at approximately ten volts or, in some cases, even less withwork gaps from half a thousandth to a few thousandths of an inch. Thecurrent densities which appear to be most satisfactory as a practicalmatter are between and 3000 amperes per square inch of effectiveelectrode area. The wattage, therefore, is between one and thirty kw.per square inch. For large areas the voltage may be reduced to fourvolts while still obtaining reasonable current density.

All prior systems with which I am familiar, which attempt to removemetal by electrolytic action, require far greater total electric energythan this to remove an equivalent amount of metal. Prior workers in thisfield have found it necessary to use voltages of the order of 100 tovolts or more with the result that the energy requirementsor in otherwords, the cost of removing the 7 metal-are of the order of ten or moretimes that required when using the invention discussed above.Furthermore, if low voltages are attempted with wide work gaps, the rateof material removal is low and thus more machines are required toproduce the same amount of work. It is apparent, therefore, thatregardless of the approach to the problem, the accomplishment of highcurrent densities with low voltages is economically essential.

Also, as previously indicated, high voltages together with comparativelylarge work gap spacings produce an electrolytic action that is far lesscontrollable, and therefore the work produced cannot be as precise asthe work produced by using the present invention.

Air jets may be used to prevent unwanted electrolytic action betweenside surfaces of the electrode and the work, where the electrode is notin close proximity to the work but where electrolyte is caught instagnant pockets. The air is used to blast away the stagnantelectrolyte. The arrangement of FIG. 1 in which the work is positionedabove the electrode is also helpful in eliminating stagnant electrolytepockets as gravity causes the electrolyte to fall away from the workarea. This is the case in forming cavities in the work. Where the partto be produced is a punch or the like so that there is a cavity in theelectrode, then the electrode is placed above the work so that gravityhelps to clear away the electrolyte except where there is close spacingbetween the electrode and the work.

A wide variety of electrolytes may be used in the apparatus andprocesses heretofore described. Some work materials respond to acidsolutions of 5% to 25% of the appropriate strong acids such ashydrochloric, nitric and sulphuric. Other materials, such as cementedcarbidese.g., tungsten, tungsten carbide, titanium carbide, etc. respondbetter to caustic solutions such as a solution of potassium hydroxide towhich may be added 5% sodium tungstate.

To the extent possible without excessive loss of removal rates, it ispreferable to use neutral or nearly neutral salt solutions because theyare much easier and safer for routine shop handling. A solution of thistype which has shown good versatility and good removal rates may be madeby adding to 15 gallons of water the following:

This solution, when supplied to, the electrode at a temperature between120 F. and 150 R, will give good removal rates on a wide variety ofsteels, including stainless steel, and also a great many of theso-called superalloys of nickel, cobalt or iron base and containing asalloying materials, in addition to those three, such materials aschromium, molybdenum, tungsten, titanium, columbium, etc.

In addition to removing material at good rates, a good finish isobtained, and particularly on the high alloy stainless steels and thesuper-alloys, a bright, reflective surface may be created where thesurface is exposed to electrolysis under conditions of pressure and highvelocity in the electrolyte, as previously explained.

I have found that an essential to good performance of an electrolyte isthat the metal salt products of electrolytic decomposition be readilysoluble. For example, aluminium is not easily worked by this processwith many electrolytes which are usable on other materials, as theanodic action forms aluminium salts which are not very soluble or notsoluble at all and form an anodic film on the work. But a simple 5% or10% solution of acetic acid yields good results because the relativelycomplex aluminium salts formed are soluble enough to be readily washedout of the work gap.

Where fine detail of pattern is to be reproduced, it is desirable to usea solutionwhich is considerably more dilute than is desirable formaximum removal rates. Thus, the quantities of salts used in the tableabove are reduced to one fourth to one sixth of the values shown for thesame amount of water. The voltage applied is also reduced. The purposeis to accentuate the difference in removal rate between those areaswhere the electrode is close to the work and those where it is moreremote. If the electrolyte is too conductive and the applied voltage istoo high, then the difference in resistance path between areas of closeproximity and others of greater spacing is not very great, and thedetail of pattern becomes blurred. Referring tothe solution in thetable, this has been used successfully in a four-to-one dilution toduplicate coin patterns in the following configuration and procedure.First, a coin is positioned oppositean electrode like that of FIG. 3,using a disc electrode of porous sintered bronze in the form of a discabout one inch in diameter and A5 inch thick. The electrolyte is pumpedat about p.s.i. through the electrode disc after passing through afilter designed to remove all particles down to five microns. Theelectrolyzing current is first connected in a sense to make theelectrode positive. The electrode is then advanced until it'very nearlytouches the coin. Thencurrent is turned on at four volts for one or twoseconds, the electrode is then advanced, and this is repeated untilample depth has been reached to embrace all of the'coin face pattern.Then the coin is removed and replaced with a piece of die steel, and thepower leads are reversed so that the electrode is now a cathode. Theelectrode is now advanced toward the steel, using a voltage of sixvolts, and again, very close proximity is used --a few ten-thousandthsof an inch of spacingand the electrode is advanced into the steel to adepth great enough to embrace the pattern. By this means, it has beenpossible to reproduce fairly fine detail, and in comparing the height ofthe coin pattern above its fiat areas with the finished steel replica,it has been possible to bring these measurementswithin less than .001inch of difference between the original coin and the steel pattern. Sofar as I am aware, such close copying by electrolytic removal'means hasnever been approached before.

.In the foregoingv description, various parameters have been describedwith respect to the apparatus components and the steps which areembodied in the method of carrying outthe present invention. In thefollowing claims it is intended that, the language used in describingthe apparatus components and the method steps be related within therange of permissible and reasonable equivalency to the description anddisclosure. For example, it has been found that reasonably good resultscan be obtained by furnishing the electrolyzing direct current withinthe range of approximately four to 15 volts. Within thisapproximaterange, and depending upon the resistance in the. work'gap,the'current density will usually be in the range of 100 to 300( or moreamperes per square inch. The resistance in the work gap is determined bythe width of the gap and'the character of the electrolyte therein. Workgaps'ofless than .001 inch, e.g., .0005 inch, and as great as, ,012inch: havebeen described. When the electrolyte 'ispumped through suchgaps at temperatures in the range of- F. to F., a pressure of severalatmospheres. mustlbe-used to inhibit bubbling or boiling of theelectrolyteand the consequent reduction of its conductivity. Therefore,the electrolyte is pumped through the gap atpressureswithin the range of50 p.s.i. to at least 200 p.s.i. to obtain high back pressure in thework gap with a resultant high electrolyte velocity through the workgap, thereby. substantially to raise the boiling point level of theelectrolyte so as to inhibit the formation of gas bubblesin theelectrolyte and to flush away the eroded workpiece material. p I Fromthe above discussion it'will be apparent that although this inventionmay be used for producing shapes and cavities of an irregular character,such that they would be extremely difficult to form by any otherprocess, the invention also has a high order of utility for replacingmore conventional machining operations when the workpiece is one of thesuper-alloys or other material which is for all practical purposes,largely non-machinable.

From the above description of my invention as embodied in severalalternative variations, it will be appreciated that many changes may bemade both in the apparatus and in the method without departing from thescope or spirit of the invention, and that the scope of the invention isto be determined from the scope of the accompanying claims.

I claim 1' 1. An electrode for use in electrolytic shaping apparatus,comprising a hollow metallic member adapted to be connected into anelectrolyzing electric circuit, said member having a working andelectrically conductive tip at one end thereof adapted to be broughtinto close spacing relationship with a metallic workpiece to be shaped,said member having an opening opposite said Working tip through which anelectrolyzing fluid is adapted to be pumped, said member having a minormetallic area contiguous to said tip and exposed laterally to providecontrolled lateral electrolytic erosion of the workpiece, said memberbeing formed of a porous metallic material, and an insulating sheathencasing and secured to said tubular member from said laterally exposedarea toward and substantially to said end of said member opposite saidWorking tip.

2. The electrode claimed in claim 1 wherein said member of" porousmetallic material is formed of sintered metal.

3. The electrode claimed in claim 1 wherein said tip has a laterallyprojecting lip to provide controlled lateral electrolytic erosion of theworkpiece.

4. The electrode claimed in claim 1 wherein said memher is tubular.

5. An electrode for use in electrolytic shaping apparatus, comprising ahollow metallic member adapted to be connected into an electrolyzingelectric circuit, said member having a working and electricallyconductive tip at one end thereof adapted to be brought into closespacing relationship with a metallic workpiece to be shaped, said memberhaving an opening opposite said working tip through which anelectrolyzing fluid is adapted to be pumped, said member being formed ofa porous metallic material.

6. The electrode claimed in claim 5 wherein said porous metallicmaterial has passages formed therein.

7. The electrode claimed in claim 5 wherein said member has a minormetallic area contiguous to said tip and exposed laterally to providecontrolled lateral electrolytic erosion of the workpiece.

8. The electrode claimed in claim 7 wherein an insulating sheath encasesand is secured to the tubular member from said laterally exposed areatoward and substantially to said end of said member opposite saidworking tip.

9. The electrode claimed in claim 5 wherein said working tip is providedwith passages therethrough and with connecting conduits to said passagesfor permitting removal of electrolyte from the Work.

10. The electrode claimed in claim 9 wherein said member is hollow forintroducing said electrolyte to said porous tip for passagetherethrough.

References Cited UNITED STATES PATENTS 2,539,455 1/1951 Mazia 204140.5

JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner US. Cl.X.R. 204224 Dedication 3,498,904.Lynn A. Williams, Winnetka, I11.ELECTRODE FOR ELEC- TROLYTIC SHAPING. Patent dated Mar. 3, 1970.Dedication filed Dec. 23, 1971, by the assignee, Anocut EngineeringCompany. Hereby dedicates to the Public the portion of the term of thepatent subsquent to Dec. 24 1971.

[Ofiiciai Gazette Ayn-i118, 1.972.

